A gas turbine engine has a turbine section and a compression section both of which have rotating and stationary components. The rotating components are included in a rotor assembly and the non-rotating components are included in a stator assembly. An annular flow path for working medium gases extends axially through the engine and passes in alternating succession between components of the stator assembly and components of the rotor assembly. The stator assembly commonly includes an outer case which circumscribes the rotor assembly and the working medium flow path. Arrays of stator vanes extend inwardly from the outer case. The stator vanes direct the flowing working medium gases to preferred angles of attack with respect to downstream rotor blades. A portion of a turbine section of one such engine is shown in FIG. 6 (Prior Art). As shown in this drawing, the rearward portion of the stator vane is retained axially by the outer case and retained radially by an annular retaining ring which is loose axially at all times with respect to the array of stator vanes and an adjacent outer air seal. The annular ring is radially stiff such that the annular ring can exert a radial force without buckling against any vanes which pivot forwardly. Such a pivoting motion may occur when an engine surges and experiences reverse flow from the exhaust section towards the inlet.
To increase the service life of components in modern engines, cooling air is also flowed through passages on the interior of the case. The cooling air removes heat from the case and from the outer air seals and stator vanes which are in intimate contact with the hot working medium gases. Often, the case forms the outer boundary of the cooling air flow path and portions of the stator vanes and the outer air seals form the inner boundary of the cooling air flow path. In the interests of engine efficiency, it is desirable to separate the cooling air flow path from the hot working medium gases. Accordingly, sealing is provided by an annular ring between an array of stator vanes and the adjacent outer air seal. For sealing to be effective the ring must accommodate relative axial and radial movement between the annular array of stator vanes and the annular outer air seal. However, adapting the ring to accommodate axial and radial movement must not be at the expense of radial stiffness which enables the ring to provide the radial retaining force to the stator vanes.